B36: Cloning
Types of cloning including cuttings, tissue culture and animal cloning
Key Definitions
Cloning: The production of genetically identical organisms. A clone is an organism that is genetically identical to its parent — it has the same DNA.
Plant Cloning
Cuttings
Cuttings involve taking a piece of stem (or leaf/root) from a parent plant and growing it into a new plant. The new plant is genetically identical to the parent. This is a cheap and quick method used by gardeners.
Example 1: Taking Cuttings
A gardener takes a stem cutting from a prized geranium. The cutting is placed in moist compost or water. Roots develop, and a new genetically identical geranium grows. This can be repeated many times to produce lots of identical plants cheaply and quickly.
Advantages: Quick, cheap, no special equipment needed. Preserves the exact characteristics of the parent plant.
Tissue Culture
Tissue culture involves taking small groups of cells (explants) from a parent plant and growing them on a nutrient medium (agar gel) containing plant hormones. This produces many identical plants and is used commercially on a large scale.
Example 2: Commercial Tissue Culture
A nursery wants to produce thousands of identical orchid plants. They take small pieces of plant tissue and place them on agar gel containing nutrients and growth hormones (auxin). The cells divide and grow into tiny plantlets, which are then transferred to soil. Many thousands of identical plants can be produced from a single parent.
Advantages: Large numbers of clones can be produced in a small space. Can be done at any time of year. Disease-free plants. Rare species can be preserved.
| Feature | Cuttings | Tissue Culture |
|---|---|---|
| Cost | Cheap | Expensive (requires lab equipment) |
| Speed | Quick | Slower (but produces many more plants) |
| Number of clones | Few at a time | Thousands from one parent |
| Equipment needed | Minimal (scissors, compost) | Sterile lab, agar, hormones |
| Use | Gardeners, small-scale | Commercial, large-scale |
Animal Cloning
Adult Cell Cloning
Adult cell cloning (somatic cell nuclear transfer) produces a clone of an adult animal. The nucleus from an adult body cell is transferred into an empty egg cell, which then develops into an embryo genetically identical to the donor of the nucleus.
1. Remove the nucleus from an egg cell (enucleation)
2. Insert the nucleus from an adult body cell (donor)
3. Give the cell an electric shock to stimulate cell division
4. The embryo develops and is implanted into a surrogate mother
5. The offspring is a clone of the donor adult
2. Insert the nucleus from an adult body cell (donor)
3. Give the cell an electric shock to stimulate cell division
4. The embryo develops and is implanted into a surrogate mother
5. The offspring is a clone of the donor adult
Example 3: Dolly the Sheep (1996)
Dolly was the first mammal cloned from an adult cell. The process:
- An egg cell was taken from a sheep and its nucleus was removed
- A body cell (udder cell) was taken from a second sheep — the donor
- The nucleus from the udder cell was inserted into the empty egg cell
- An electric shock stimulated the cell to divide, forming an embryo
- The embryo was implanted into a surrogate mother sheep
- Dolly was born — genetically identical to the donor sheep
Embryo Cloning
Embryo cloning involves splitting an early-stage embryo (before cells have specialised) into separate cells. Each cell develops into a separate embryo. The embryos are implanted into surrogate mothers and develop into genetically identical offspring.
Example 4: Embryo Cloning in Cattle
A prize bull and a prize cow are bred together. The fertilised egg divides to form an embryo with 8 cells. The embryo is split into 8 separate cells, and each one is implanted into a surrogate mother. Each calf is genetically identical to the others. This allows farmers to produce multiple copies of valuable animals from one mating.
Advantages and Disadvantages of Cloning
| Advantages | Disadvantages |
|---|---|
| Preserve endangered species | Reduced genetic variation — all clones are susceptible to the same diseases |
| Produce many organisms with desirable traits (e.g. high-yield crops) | Cloned animals often have health problems and shorter lifespans |
| Tissue culture can produce disease-free plants in large numbers | Unethical — some argue cloning animals is morally wrong |
| Research — study genetic diseases and test medicines | Risk of unknown long-term effects |
| Embryo cloning increases number of offspring from prize animals | Low success rate — many cloned embryos do not survive |
Comparison: Plant Cloning Methods
| Feature | Cuttings | Tissue Culture |
|---|---|---|
| Method | Stem/leaf piece grown in compost or water | Small cell samples grown on agar with hormones |
| Number produced | A few at a time | Thousands from one parent |
| Cost | Very cheap | Expensive (sterile lab needed) |
| Speed | Fast — weeks | Slower but more productive overall |
| Main use | Home gardeners | Commercial nurseries, conservation |
| Both produce | Genetically identical clones of the parent plant | |
Practice Questions
Q1: Foundation Describe the difference between producing plants by cuttings and by tissue culture.
Q2: Foundation Describe the process of adult cell cloning used to create Dolly the sheep.
Q3: Foundation Give two advantages and two disadvantages of cloning animals.
Q4: Higher In the cloning of Dolly the sheep, explain which sheep Dolly was genetically identical to, and why she was not identical to the egg cell donor or the surrogate mother.
Q5: Higher Explain why cloning endangered species might not be the best solution for their long-term survival.
Answers
- Cuttings involve taking a piece of stem from a parent plant and growing it directly into a new plant. It is cheap and quick but produces few plants at a time. Tissue culture involves taking small groups of cells from a parent plant and growing them on agar with hormones. It is more expensive and requires lab equipment but can produce thousands of identical plants in a small space.
- 1. The nucleus was removed from an egg cell taken from one sheep. 2. A nucleus from an adult body cell (udder cell) was taken from a second sheep (the donor). 3. The donor nucleus was inserted into the empty egg cell. 4. An electric shock stimulated the cell to start dividing, forming an embryo. 5. The embryo was implanted into a surrogate mother sheep. 6. Dolly was born — genetically identical to the donor sheep that provided the body cell nucleus.
- Advantages: 1) Can preserve endangered species by increasing their numbers. 2) Can produce many copies of animals with desirable traits (e.g. high milk production). Disadvantages: 1) Reduced genetic variation — all clones are vulnerable to the same diseases. 2) Cloned animals often have health problems and shorter lifespans.
- Dolly was genetically identical to the donor sheep that provided the body cell nucleus. This is because the nucleus contains all the genetic information, and Dolly received her nucleus from this donor. The egg cell donor only contributed the empty egg cell (no genetic material, as the nucleus was removed). The surrogate mother only provided a womb for the embryo to develop — she did not contribute any genetic material.
- Cloning produces genetically identical individuals, which means the population has no genetic variation. Without genetic variation, the species cannot adapt to environmental changes through natural selection. Additionally, if a disease arises that one clone is susceptible to, all clones will be susceptible — potentially wiping out the entire population. For long-term survival, maintaining genetic diversity through habitat conservation and natural breeding is more effective.
Exam Tips
- Know the difference between the two plant methods: cuttings (cheap, simple, few plants) vs tissue culture (expensive, complex, many plants). Both produce genetically identical clones
- For adult cell cloning, remember the steps in order: remove nucleus from egg → insert donor nucleus → electric shock → embryo → surrogate. The clone is genetically identical to the DONOR of the nucleus, NOT the egg cell donor or the surrogate mother
- Don’t confuse adult cell cloning with embryo cloning — adult cell cloning uses a nucleus from an adult body cell; embryo cloning splits an early embryo
- When evaluating cloning, always mention the reduced genetic variation problem and explain why it matters (vulnerability to disease, inability to adapt)
🔢 Maths Skills
Mathematical Skills
Calculating the number of clones produced: if tissue culture produces 8 plantlets per explant and a nursery starts with 20 explants, total clones = 8 × 20 = 160. If each plantlet can itself be subdivided 3 times, the total becomes 20 × 8³ = 20 × 512 = 10,240 plants.
⚠️ Common Misconceptions
Watch Out!
Students often think clones are identical in every way. Wrong: Clones are always identical in every way Correct: Clones have the same DNA but environmental differences cause variation (e.g. identical twins can differ in weight, scars, personality)
Students often think adult cell cloning means cloning adult humans. Wrong: Adult cell cloning means cloning humans Correct: It refers to using a nucleus from an adult body cell (e.g. Dolly the sheep was cloned from an udder cell — the “adult” refers to the cell source, not the species)
✍️ 6-Mark Question
Extended Answer
6 marks: Compare the methods of cloning plants and animals, and discuss the advantages and disadvantages of cloning.
Plant cloning methods include cuttings (cheap, quick, few plants at a time) and tissue culture (expensive, produces thousands in sterile lab conditions). Animal cloning includes adult cell cloning (nucleus from an adult body cell transferred to an enucleated egg, electric shock, embryo implanted in surrogate — e.g. Dolly) and embryo cloning (splitting an early embryo into separate cells, each implanted into a surrogate). Advantages: can preserve endangered species; produce many organisms with desirable traits; tissue culture produces disease-free plants in large numbers; embryo cloning increases offspring from prize animals. Disadvantages: reduced genetic variation makes all clones vulnerable to the same diseases; cloned animals often have health problems and shorter lifespans; low success rate; ethical concerns about animal welfare.
Mark scheme: 1 mark per cloning method described (up to 2), 1 mark per advantage (up to 2), 1 mark per disadvantage (up to 2)
📊 AO3: Analyse & Evaluate
Analysis and Evaluation
Conservationists are considering cloning the northern white rhino (only 2 individuals remain, both female). Evaluate whether cloning is a viable long-term solution for saving this species. Consider genetic diversity, welfare, and alternative approaches.
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